[The collateral venous blood flow and the surgical procedure in parasagittal meningiomas].

Peculiarities of the collateral venous bloodflow were analysed in 242 cases of parasagittal meningiomas (PM). The cerebral veins participated in collateral bloodflow in 52.1% of cases with tumours of the anterior third of the superior sagittal sinus (SSS), whereas in 39% of such cases the retrograde flow through proximal SSS have been found. Neoplasms of the middle/posterior third of SSS led to the collateral venous bloodflow through the anastomoses of the cerebral veins in 67% of cases. In 56% of patients the collateral flow was through extracerebral veins. The absence of strict conformities in the development of the collateral venous bloodflow leads to necessity of its intraoperative control by EEG monitoring. Severe changes of bioelectrical activity (14.9% of cases) are an indication for division of the surgical procedure into several stages.